1. Related Art Statement
The present invention relates to an automatic ultrasonic testing method for automatically detecting internal flaws in articles such as solid-core station post insulators and long-rod insulators, in which ultrasonic noises are generated in ultrasonic testing waveforms.
2. Prior Art
In the manufacturing steps of solid-core station post insulators or long-rod insulators, prior to assembling metal fittings with cement to upper and lower edges of a porcelain body, it is necessary to effect an ultrasonic test with respect to these upper and lower edges to detect any internal flaws. However, since the porcelain body always includes a plurality of porcelain shed portions, many echoes are generated due to the plurality of sheds. Therefore, even if the porcelain body is normal, ultrasonic noises such as those shown in FIGS. 4, 7 and 8 are generated in the ultrasonic testing waveforms. In this case, if the porcelain body has internal flaws, a flaw echo is shown by A in FIG. 5 or B in FIG. 6 in the ultrasonic testing waveform.
Usually, workers can easily visually detect the flaw echoes in the ultrasonic testing waveform, however, it is often very difficult to usually detect such flaw echoes by the naked eye, and thus it is likely that detection of the flaw echoes will vary from worker to worker. Therefore, it is required that detection of the flaw echoes be automated.
In a known normal automatic ultrasonic testing method, a slice level C shown in FIG. 5 is set at an arbitrary position in a wave image on a CRT, and an echo height beyond the slice level is detected as the flaw echo. However, in this method, since the slice level must be set beyond a maximum value of the ultrasonic noises as shown in FIG. 5, a flaw echo having an echo height below that of the ultrasonic noises as shown in FIG. 6 can not be detected.
Moreover, a method has been known in which a standard waveform including ultrasonic noises is set previously, and a flaw echo is automatically detected by comparing it with the standard waveform. However, in this method, it is very difficult to set the standard waveform because of the two reasons mentioned below.
First, since the ultrasonic noises change from the state shown in FIG. 4 to the state described in FIG. 7 as a result of a little variation in location of a probe, heights of adjacent pulses are partially shown in an inverse manner.
Second, since some positions generate ultrasonic noises such as shown in FIG. 8, it is extremely difficult to set the reasonable standard waveform.
Therefore, heretofore an automatic ultrasonic testing method has not been utilized for the articles such as insulators in which the ultrasonic noises are liable to be generated.